-3m(m+8)

A) -3m²+24

B) -3m²-24m

C) -24m²

D) -4m+5

B) -3m²-24m

To simplify the expression -3m(m+8), we'll use the distributive property.

Step 1: Distribute -3m to both terms in the parentheses:
-3m * m = -3m²
-3m * 8 = -24m

The simplified expression is then -3m² - 24m.

Therefore, the correct answer is B) -3m² - 24m.